A Unidirectional Single-Phase LLC Based High Frequency Link Inverter

This paper presents a resonant LLC based isolated single-phase DC-AC converter for grid connected photovoltaic systems. The converter employs a LLC DC-rectified AC stage followed by a line frequency unfolder. A constant switching frequency based modulation strategy is used to generate sinusoidal output voltage. The gain of the converter is independent of the load current in the operating region. To control active power flow, a small variation in gain is needed which results in small variation in operating frequency. This ensures optimal design of the magnetic components. A closed form expression of the converter voltage gain is derived. Additionally, load independent ZVS of the input H-bridge is ensured. A 2 kW prototype is designed and key simulation and experimental results are presented to verify the converter operation.